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<head>
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    <title>WebGL - Textures - Mips - Depth</title>
    <link type="text/css" href="../resources/webgl-tutorials.css" rel="stylesheet" />
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        #ui {
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            background-color: red;
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<body>
    <div id="info">
        <div class="description">
            Show how mips are important for depth<br />
        </div>
        <a href="https://webglfundamentals.org/webgl/lessons/zh_cn/webgl-3d-textures.html" target="_blank">WebGL
            三维纹理</a>
    </div>
    <canvas id="canvas"></canvas>
    <div id="uiContainer">
        <div id="ui">
            <div id="b">Click to switch texture</div>
        </div>
    </div>
</body>
<!-- vertex shader -->
<script id="3d-vertex-shader" type="x-shader/x-vertex">
attribute vec4 a_position;
attribute vec2 a_texcoord;

uniform mat4 u_matrix;

varying vec2 v_texcoord;

void main() {
  // Multiply the position by the matrix.
  gl_Position = u_matrix * a_position;

  // Pass the texcoord to the fragment shader.
  v_texcoord = a_texcoord;
}
</script>
<!-- fragment shader -->
<script id="3d-fragment-shader" type="x-shader/x-fragment">
precision mediump float;

// Passed in from the vertex shader.
varying vec2 v_texcoord;

// The texture.
uniform sampler2D u_texture;

void main() {
   gl_FragColor = texture2D(u_texture, v_texcoord);
}
</script>
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for most samples webgl-utils only provides shader compiling/linking and
canvas resizing because why clutter the examples with code that's the same in every sample.
See http://webglfundamentals.org/webgl/lessons/webgl-boilerplate.html
and http://webglfundamentals.org/webgl/lessons/webgl-resizing-the-canvas.html
for webgl-utils, m3, m4, and webgl-lessons-ui.
-->
<script src="../resources/webgl-utils.js"></script>
<script src="../resources/m4.js"></script>
<script>
    "use strict";

    var zDepth = 50;

    function main() {
        // Get A WebGL context
        var canvas = document.getElementById("canvas", { antialias: false });
        var gl = canvas.getContext("webgl");
        if (!gl) {
            return;
        }

        // setup GLSL program
        var program = webglUtils.createProgramFromScripts(gl, ["3d-vertex-shader", "3d-fragment-shader"]);

        // look up where the vertex data needs to go.
        var positionLocation = gl.getAttribLocation(program, "a_position");
        var texcoordLocation = gl.getAttribLocation(program, "a_texcoord");

        // lookup uniforms
        var matrixLocation = gl.getUniformLocation(program, "u_matrix");
        var textureLocation = gl.getUniformLocation(program, "u_texture");

        // Create a buffer for positions
        var positionBuffer = gl.createBuffer();
        // Bind it to ARRAY_BUFFER (think of it as ARRAY_BUFFER = positionBuffer)
        gl.bindBuffer(gl.ARRAY_BUFFER, positionBuffer);
        // Put the positions in the buffer
        setGeometry(gl);

        // provide texture coordinates for the rectangle.
        var texcoordBuffer = gl.createBuffer();
        gl.bindBuffer(gl.ARRAY_BUFFER, texcoordBuffer);
        // Set Texcoords.
        setTexcoords(gl);

        // Create a texture with different colored mips
        var mipTexture = gl.createTexture();
        gl.bindTexture(gl.TEXTURE_2D, mipTexture);
        var c = document.createElement("canvas");
        var ctx = c.getContext("2d");
        var mips = [
            { size: 64, color: "rgb(128,0,255)", },
            { size: 32, color: "rgb(0,0,255)", },
            { size: 16, color: "rgb(255,0,0)", },
            { size: 8, color: "rgb(255,255,0)", },
            { size: 4, color: "rgb(0,255,0)", },
            { size: 2, color: "rgb(0,255,255)", },
            { size: 1, color: "rgb(255,0,255)", },
        ];
        mips.forEach(function (s, level) {
            var size = s.size;
            c.width = size;
            c.height = size;
            ctx.fillStyle = "rgb(255,255,255)";
            ctx.fillRect(0, 0, size, size);
            ctx.fillStyle = s.color;
            ctx.fillRect(0, 0, size / 2, size / 2);
            ctx.fillRect(size / 2, size / 2, size / 2, size / 2);
            gl.texImage2D(gl.TEXTURE_2D, level, gl.RGBA, gl.RGBA, gl.UNSIGNED_BYTE, c);
        });

        // Create a texture.
        var texture = gl.createTexture();
        gl.bindTexture(gl.TEXTURE_2D, texture);
        // Fill the texture with a 1x1 blue pixel.
        gl.texImage2D(gl.TEXTURE_2D, 0, gl.RGBA, 1, 1, 0, gl.RGBA, gl.UNSIGNED_BYTE,
            new Uint8Array([0, 0, 255, 255]));
        // Asynchronously load an image
        var image = new Image();
        image.src = "../resources/mip-low-res-example.png";
        image.addEventListener('load', function () {
            // Now that the image has loaded make copy it to the texture.
            gl.bindTexture(gl.TEXTURE_2D, texture);
            gl.texImage2D(gl.TEXTURE_2D, 0, gl.RGBA, gl.RGBA, gl.UNSIGNED_BYTE, image);
            gl.texParameteri(gl.TEXTURE_2D, gl.TEXTURE_WRAP_S, gl.CLAMP_TO_EDGE);

            // Check if the image is a power of 2 in both dimensions.
            if (isPowerOf2(image.width) && isPowerOf2(image.height)) {
                // Yes, it's a power of 2. Generate mips.
                gl.generateMipmap(gl.TEXTURE_2D);
            } else {
                // No, it's not a power of 2. Turn of mips and set wrapping to clamp to edge
                gl.texParameteri(gl.TEXTURE_2D, gl.TEXTURE_WRAP_S, gl.CLAMP_TO_EDGE);
                gl.texParameteri(gl.TEXTURE_2D, gl.TEXTURE_WRAP_T, gl.CLAMP_TO_EDGE);
                gl.texParameteri(gl.TEXTURE_2D, gl.TEXTURE_MIN_FILTER, gl.LINEAR);
            }
            drawScene();
        });

        var textures = [
            texture,
            mipTexture,
        ];
        var textureIndex = 0;

        document.body.addEventListener('click', function () {
            textureIndex = (textureIndex + 1) % textures.length;
            drawScene();
        });

        function isPowerOf2(value) {
            return (value & (value - 1)) === 0;
        }

        function radToDeg(r) {
            return r * 180 / Math.PI;
        }

        function degToRad(d) {
            return d * Math.PI / 180;
        }

        var fieldOfViewRadians = degToRad(60);

        drawScene();

        // Draw the scene.
        function drawScene() {
            webglUtils.resizeCanvasToDisplaySize(gl.canvas);

            // Tell WebGL how to convert from clip space to pixels
            gl.viewport(0, 0, gl.canvas.width, gl.canvas.height);

            gl.enable(gl.CULL_FACE);
            gl.enable(gl.DEPTH_TEST);

            // Clear the framebuffer texture.
            gl.clearColor(0, 0, 0, 1);
            gl.clear(gl.COLOR_BUFFER_BIT | gl.DEPTH_BUFFER_BIT);

            // Tell it to use our program (pair of shaders)
            gl.useProgram(program);

            // Turn on the position attribute
            gl.enableVertexAttribArray(positionLocation);

            // Bind the position buffer.
            gl.bindBuffer(gl.ARRAY_BUFFER, positionBuffer);

            // Tell the position attribute how to get data out of positionBuffer (ARRAY_BUFFER)
            var size = 3;          // 3 components per iteration
            var type = gl.FLOAT;   // the data is 32bit floats
            var normalize = false; // don't normalize the data
            var stride = 0;        // 0 = move forward size * sizeof(type) each iteration to get the next position
            var offset = 0;        // start at the beginning of the buffer
            gl.vertexAttribPointer(
                positionLocation, size, type, normalize, stride, offset);

            // Turn on the teccord attribute
            gl.enableVertexAttribArray(texcoordLocation);

            // Bind the position buffer.
            gl.bindBuffer(gl.ARRAY_BUFFER, texcoordBuffer);

            // Tell the position attribute how to get data out of positionBuffer (ARRAY_BUFFER)
            var size = 2;          // 2 components per iteration
            var type = gl.FLOAT;   // the data is 32bit floats
            var normalize = false; // don't normalize the data
            var stride = 0;        // 0 = move forward size * sizeof(type) each iteration to get the next position
            var offset = 0;        // start at the beginning of the buffer
            gl.vertexAttribPointer(
                texcoordLocation, size, type, normalize, stride, offset);

            // Compute the projection matrix
            var aspect = gl.canvas.clientWidth / gl.canvas.clientHeight;
            var zNear = 1;
            var zFar = 2000;
            var projectionMatrix =
                m4.perspective(fieldOfViewRadians, aspect, zNear, zFar);

            var cameraPosition = [0, 0, 2];
            var up = [0, 1, 0];
            var target = [0, 0, 0];

            // Compute the camera's matrix using look at.
            var cameraMatrix = m4.lookAt(cameraPosition, target, up);

            // Make a view matrix from the camera matrix.
            var viewMatrix = m4.inverse(cameraMatrix);

            var viewProjectionMatrix = m4.multiply(projectionMatrix, viewMatrix);

            var settings = [
                { x: -1, y: 1, zRot: 0, magFilter: gl.NEAREST, minFilter: gl.NEAREST, },
                { x: 0, y: 1, zRot: 0, magFilter: gl.LINEAR, minFilter: gl.LINEAR, },
                { x: 1, y: 1, zRot: 0, magFilter: gl.LINEAR, minFilter: gl.NEAREST_MIPMAP_NEAREST, },
                { x: -1, y: -1, zRot: 1, magFilter: gl.LINEAR, minFilter: gl.LINEAR_MIPMAP_NEAREST, },
                { x: 0, y: -1, zRot: 1, magFilter: gl.LINEAR, minFilter: gl.NEAREST_MIPMAP_LINEAR, },
                { x: 1, y: -1, zRot: 1, magFilter: gl.LINEAR, minFilter: gl.LINEAR_MIPMAP_LINEAR, },
            ];
            var xSpacing = 1.2;
            var ySpacing = 0.7;
            settings.forEach(function (s) {
                gl.bindTexture(gl.TEXTURE_2D, textures[textureIndex]);
                gl.texParameteri(gl.TEXTURE_2D, gl.TEXTURE_MIN_FILTER, s.minFilter);
                gl.texParameteri(gl.TEXTURE_2D, gl.TEXTURE_MAG_FILTER, s.magFilter);

                var matrix = m4.translate(viewProjectionMatrix, s.x * xSpacing, s.y * ySpacing, -zDepth * 0.5);
                matrix = m4.zRotate(matrix, s.zRot * Math.PI);
                matrix = m4.scale(matrix, 1, 1, zDepth);

                // Set the matrix.
                gl.uniformMatrix4fv(matrixLocation, false, matrix);

                // Tell the shader to use texture unit 0 for u_texture
                gl.uniform1i(textureLocation, 0);

                // Draw the geometry.
                gl.drawArrays(gl.TRIANGLES, 0, 1 * 6);
            });
        }
    }

    // Fill the buffer with the values that define a plane.
    function setGeometry(gl) {
        var positions = new Float32Array(
            [
                -0.5, 0.5, -0.5,
                0.5, 0.5, -0.5,
                -0.5, 0.5, 0.5,
                -0.5, 0.5, 0.5,
                0.5, 0.5, -0.5,
                0.5, 0.5, 0.5,

            ]);
        gl.bufferData(gl.ARRAY_BUFFER, positions, gl.STATIC_DRAW);
    }

    // Fill the buffer with texture coordinates for a plane.
    function setTexcoords(gl) {
        gl.bufferData(
            gl.ARRAY_BUFFER,
            new Float32Array(
                [
                    0, 0,
                    1, 0,
                    0, zDepth,
                    0, zDepth,
                    1, 0,
                    1, zDepth,

                ]),
            gl.STATIC_DRAW);
    }

    main();
</script>

</html>